Sdma Channels - Freescale Semiconductor MPC850 User Manual

Chapter 19
SDMA Channels and IDMA Emulation
The CPM controls two physical serial DMA (SDMA) channels on the MPC850. Using the
two physical channels, the CP implements 20 virtual SDMA channels, each dedicated to a
serial controller transmitter or receiver—eight for the USB, four for the full-duplex SCCs,
and the remaining eight for the SPI, I
general-purpose independent DMA (IDMA) channels for memory/memory and
peripheral/memory transfers using the two physical SDMA channels.

19.1 SDMA Channels

Data from the USB, the SCCs, SMCs, SPI, and I
(path 1) or the internal dual-port RAM (path 2), as shown in Figure 19-1. On a path 1
access, the SDMA channel must acquire both the U-bus and the external system bus. On a
path 2 access, the data transfer occurs only on the U-bus, independent of the external
system bus unless the SIU is configured in show-cycles mode. Thus, in normal operation,
U-bus transfers occur simultaneously with external system bus operations.
PowerPC
Core
Communications
Processor
(CP)
USB SCC2
2
C, and the two SMCs. The CPM also emulates two
Internal U-Bus
SDMA
SCC3 SMC1
Figure 19-1. MPC850 SDMA Data Paths
Chapter 19. SDMA Channels and IDMA Emulation
2
C can be routed to external memory
1
System
Interface
Unit
(SIU)
2
Dual-Port
RAM
SMC2 SPI
External
RAM
System Bus
External
ROM
2
I C